Active-matrix type liquid crystal display panels are formed using active-matrix liquid crystal display substrates which comprise pixel electrodes for each pixel element, arranged in a matrix pattern, gate lines which are common to all pixel electrodes, source lines, and thin film transistors. Generally, in this type of liquid crystal display panel, after the manufacture of an active matrix liquid crystal display substrate, by a transparent substrate, or the like, is disposed above the active matrix liquid crystal display substrate separated by a spacer, and the gap formed between the active matrix liquid crystal display substrate and the transparent substrate is filled with liquid crystal.
In liquid crystal televisions which are presently produced using this technique, there are many units which reach a pixel count of 250,000-500,000. Some have reached the market having a pixel count of over 1,000,000.
Formation of the pixels, and the numerous lines thereto corresponding, on a substrate, involve various formation processes which are carried out in a clean room. The clean room is controlled so that there is very little dust contained therein. However, when the pixels or the line width is extremely small, the presence of a small amount of microdust in the manufacturing atmosphere is directly linked to open-circuit or short-circuit defects of the pixel electrodes, gate lines or source lines. Presently, up to ten such defects are permitted. It is common to classify products as defective if the number of defects exceeds ten.
With present manufacturing technology, it is extremely difficult to reduce the number of such defects below the permitted limit, so that especially in liquid crystal display panels having a large number of pixels, the rate of defective products is startlingly high.
Present testing uses a probe to test active matrix liquid crystal display substrates when manufacturing is completed. When the number of elements on the active matrix liquid crystal display substrate is very large, an excessive amount of time is required for testing, and this approach becomes impractical.
Because of this, when liquid crystal display panels using active matrix liquid crystal display substrates are manufactured, testing was not carried out on the production line of the active matrix liquid crystal display substrates. After the completion of manufacturing, electrical power was applied to the liquid crystal display panel, and it was determined by eye whether each pixel was actuated or not. Even if defects were detected at this point, they were difficult to repair, and liquid crystal display panels were rejected and disposed of. This was a large cause of the extremely poor yield of active matrix liquid crystal displays.